The present invention relates to methods for monitoring and controlling biological activity in wastewater and controlling the treatment thereof. Specifically a method has been developed that correlates the production of polyhydroxyalkanoates (PHA) with bioreactor health and biocatalytic efficiency.
A number of devices and systems to process and purify water from industrial operations and municipal sources prior to discharging the water are known. Activated-sludge wastewater treatment plants, which are well known in the art, have been most often utilized to address this problem. Additionally, many industrial and municipal water treatment plants utilize biological systems to pre-treat their wastes prior to discharging into the usual municipal treatment plant. In these processes, the microorganisms used in the activated sludge break down or degrade contaminants for the desired water treatment. Efficient process performance and control requires quick and accurate assessment of information on the activity of microorganisms. This has proven to be a difficult task in view of the wide variety of materials and contaminants that typically enter into treatment systems. Variations in the quantity of wastewater being treated, such as daily, weekly or seasonal changes, can dramatically change numerous important factors in the treatment process, such as pH, temperature, nutrients and the like, the alteration of which can be highly detrimental to proper wastewater treatment. Improperly treated wastewater poses serious human health dangers. It is imperative therefore to maintain the health and biocatalytic efficiency of these activated sludge systems.
Various biological processes are currently used in wastewater treatment plants to assist in contamination degradation. In a typical process, contaminants in the wastewater, such as carbon sources (measured as biological oxygen demand or BOD), ammonia, nitrates, phosphates and the like are digested by the activated sludge in anaerobic, anoxic and aerobic stages, also known in the art. In the anaerobic stage, the wastewater, with or without passing through a preliminary settlement process, is mixed with return activated sludge.
The goal of wastewater bioreactors is to mineralize inlet organic and inorganic compounds (nitrogen oxides e.g., nitrate, nitrite, and ammonia) to carbon dioxide and nitrogen gas resulting in a clean effluent stream. The efficiency of industrial wastewater treatment systems is especially important since loss of performance/capacity to treat process wastewater translates to lower manufacturing up time. Presently, there are no rapid methods to assess the biocatalytic capacity of wastewater reactors.
Currently, crude macroscopic parameters are used to gauge the performance of wastewater bioreactors. These crude macroscopic parameters include: exit carbon as measured by COD (chemical oxygen demand) or TOC (Total Organic Carbon); exit nitrogen by Total Kjeldahl Nitrogen (TKN) and exit phosphate by Ion Chromotography. While measurements of effluent leakage of exogenously supplied carbon, such as methanol and organic acid, could be used to identify an impaired bioreactor, these compounds would not be reliable indicators of bioreactor health because many other processes can impact the amount of carbon removed. Furthermore, assessment of performance using these metrics results in a responsive operating strategy, i.e., changes to reactor loads that are made only after deviation from the desired performance is observed. Finally, the catalytic activity of the biomass present in the bioreactors is time consuming to measure. For example, the denitrification rate is determined by removing biomass from the reactor and performing a batch rate study; taking about 1-2 days to perform, and therefore cannot be used to gauge the current denitrification capacity of the reactor. These batch studies are useful in establishing long term performance characteristics. To date, there have been no reports describing the relationship between cell physiology and catalytic capacity wastewater bioreactors.
The above methods are useful for monitoring the health of activated sludge systems however they contain several drawbacks including the inability to accurately predict a reduction or loss of denitrification activity in the system before nitrate or one of the denitrification intermediates is present in the bioreactor. This results in nitrate leakage or incomplete denitrification that is highly detrimental and undesirable to such systems. An improved method of tracking biocatalytic efficiency is needed, particularly with respect to denitrification potential.
The problem to be solved, therefore is to provide a facile, highly responsive method of monitoring activated sludge environments to rapidly predict loss of denitrification activity and other indicators of biocatalytic efficiency such as the concentrations of nitrate, ammonia, sulfate, phosphate and carbon dioxide in the system.
The present invention provides reliable methods to monitor bioreactor health and to maintain viable cultures within the bioreactor. Specifically, Applicants have solved the above-stated problem by making the correlation between the production of an internal storage molecule and denitrification rate as a control strategy. This internal storage molecule may be a class of storage molecules, collectively termed polyhydroxyalkanoates (PHA), or glycogen or the like. Preferably, this internal storage molecule is polyhydroxyalkanoates (PHA). The PHA level in the bacteria of the activated sludge can be easily measured and controlled by the level of nutrients (ammonia, phosphate, sulfate) in the bioreactor.
Specifically, the present invention provides a method for monitoring and controlling the biocatalytic efficiency of a wastewater treatment process comprising: a) providing an activated sludge environment comprising:
(i) a carbon influx;
(ii) cultures of autotrophic, heterotrophic and facultative microorganisms;
(iii) feed nutrients; and
(iv) an end electron acceptor; b) sampling wastewater from anaerobic, anoxic and/or aerobic stages of the treatment process; c) measuring the concentration of polyhydroxyalkanoates present in the sample to determine the status of selected sample characteristics; and d) adjusting the feed nutrients in the activated sludge environment depending on the status of the selected sample as measured in c), whereby the biocatalytic efficiency of a wastewater treatment process is controlled.
An indication that the biocatalytic efficiency of the wastewater treatment process is impaired is seen when the polyhydroxyalkanoates concentration is greater than about 15 to about 20 dry weight percent of the biomass. Preferably, the feed nutrients are adjusted accordingly in the activated sludge environment when the PHA concentration is from about 10 to about 20 dry weight percent of the biomass. More preferably, the feed nutrients are adjusted accordingly in the activated sludge environment when the PHA concentration is from about 10 to about 15 dry weight percent of the biomass.
Sample characteristics are selected from the group consisting of efficiency of denitrification, nitrate concentration, ammonia concentration, sulfate concentration, phosphate concentration and carbon dioxide concentration. Similarly, feed nutrients are selected from the group consisting of nitrate, ammonia, sulfate, sulfide, urea and phosphate. In addition, an end electron acceptor is selected from the group consisting of oxygen, nitrate, nitrite, nitrous oxide, ferric oxide, and sulfate.
The invention additionally provides a method of maintaining viable cultures in an activated sludge environment in the absence of carbon influx comprising: a) providing an activated sludge environment comprising:
(i) a carbon influx;
(ii) cultures of autotrophic, heterotrophic and facultative microorganisms;
(iii) feed nutrients; and
(iv) an end electron acceptor; b) removing the feed nutrients from the activated sludge environment while continuously monitoring the concentration of polyhydroxyalkanoates present in the activated sludge environment; c) removing the carbon influx from the activated sludge environment when the concentration of polyhydroxyalkanoates is greater than about 15 to about 20 dry weight percent of the biomass; and d) adding a minimal concentration of nitrate to the activated sludge environment of step c); whereby the cultures of autotrophic, heterotrophic and facultative microorganisms are maintained in a viable state in the absence of a carbon influx.
In a preferred embodiment, the carbon influx is removed from the activated sludge environment when the concentration of PHA is about 20 dry weight percent of biomass or greater.
In another preferred embodiment, the minimal concentration of nitrate added to the activated sludge environment of step c) is based on the COD content of the PHA in the biomass. Specifically, the COD provided by the PHA is equal to the fraction of PHA times the total dry biomass times fraction of carbon in PHA times the conversion factor for TOC to COD and is represented by Equation 1.
PHA COD(mg/L)=(0.2 mg PHA/mg MLSS)xc3x97[MLSS(mg/L)]xc3x97(0.556 mg C/mg PHA)xe2x80x83xe2x80x83EQUATION 1:
The amount of nitrate that can be added to the activated sludge environment is equal to the COD provided by the PHA multiplied by the amount of nitrate-N reduced/COD)xc3x97(4.5 mg nitrate/mg nitrate-N).